1. Field of the Invention
The present invention relates to an X-ray focusing instrument and an X-ray analysis apparatus.
2. Description of the Related Arts
Portable X-ray analysis apparatuses are required to be compact and lightweight. Hence, the apparatus structure typically tends toward simplicity, which makes it difficult to analyze light elements and trace elements.
X-ray fluorescence beam analysis belongs to the X-ray analyses. With X-ray fluorescence beam analysis, the primary X-ray beam from X-ray radiation source is irradiated at the specimen, and excites the atoms of the specimen to generate the X-ray fluorescence beam. This X-ray fluorescence beam is to be detected by the X-ray detector. Then analysis of the element of the specimen is to be made based on the result of the detection. The apparatus using cylindrical analyzing elements was suggested for this purpose (Cf. Japan Patent Laid-open Pub. No. Hei11-23797). Under this conventional technique, it is possible to analyze the specific trace elements with high sensitivity, as the primary X-ray beam, monochromatic by analyzing element, is irradiated at the specimen.
However, the above conventional technique is not appropriate to analyze the light elements, such as sodium or magnesium, for with this technique the primary X-ray beam is to become monochromatic, it has no low-energy spectrum in it.
Furthermore, though this technique intends enlargement of the area of the analyzing surface by using cylindrical analyzing elements, the area does not become large enough as expected, as the axial length effective for the analysis is too short. Hence, the strength of the monochromatic light obtained is too low; it is difficult to analyze trace heavy elements with good sensitivity.
In addition, this technique uses so-called side window type X-ray tube. In such a case, scattering electrons should be scattered from the target, which has electric potential at the earth point. Hence, if the window material (beryllium layer) is thin, it will be distorted and cracked by the heat. So, thick beryllium layer with the thickness of 0.5 mm or more is generally used as the window material. Under such condition, it becomes impossible to analyze light elements, as low-energy spectrum of the primary X-ray is to be absorbed into the window material,
The present invention was conceived to solve the above problems involved in the prior art. It is therefore the object to provide an X-ray focusing instrument and an X-ray analysis apparatus, small enough as portable apparatuses, and at the same time, appropriate for analyses of light elements and trace heavy elements.
The above object is attained by a first aspect of the present invention. The X-ray focusing instrument focuses some of X-ray beams emitted from the X-ray radiation source on the specimen. The X-ray focusing instrument is provided with an annular analyzing element and a collimator. The analyzing element has an inner periphery, which analyzes and reflects the incident X-ray beam. The collimator has a surface which reflects the X-ray beam totally and irradiates the specimen with parallel beam. The collimator is to be set in the internal space defined by the inner periphery of the analyzing element. The analyzing element and collimator are arranged so that the axis of the annular analyzing element and that of collimator can substantially coincide with each other.
To use this X-ray focusing instrument, it is necessary to place the shield member which screens the incident primary X-ray beam in the collimator or the primary X-ray emitted from the collimator on the path of the X-ray beam. This shield member should be freely inserted or removed.
In the case of analyzing heavy elements, it is required to insert the shield member on the path of the primary X-ray beam. By this process, only the monochromatic primary X-ray beam can reach the specimen. As the excitation X-ray beam does not contain the noise, it is possible to analyze trace heavy elements with good sensitivity.
In the case of analyzing light elements, it is required to remove the shield member. The X-ray beam analyzed by the analyzing element as well as the primary X-ray beam which includes the continuous X-ray focused by the collimator is to be focused on the small area of the specimen. Thus, the primary X-ray beam obtained includes low-energy spectrum, which enables analysis of light elements.
By using this X-ray focusing instrument, it becomes possible to analyze both light and trace heavy elements selectively.
In a preferred embodiment of the present invention, the inner periphery of the analyzing element is to be formed into a barrel shape curving along the axis. This barrel shape enables the enlargement of the effective area of the analyzing element by about 70 times compared to the area obtained by the conventional technique, which uses the cylindrical analyzing element. Hence, the intensity of the X-ray beam becomes 70 times larger, as well (in the case of using energy of 20 keV and lithium fluoride as the monochromator crystal). Thus, it becomes possible to analyze trace heavy elements with good sensitivity.
In another preferred embodiment of the present invention, the above analyzing element is formed in the first circular tube; the collimator is to be formed in the second cylindrical tube; and the path of the incident X-ray beam from the X-ray radiation source on the analyzing element and that of the X-ray beam emitted from the analyzing element toward the specimen is to be formed between these two tubes.
Thus, there is no need to place a slit additionally, for the path of the X-ray beam is formed between the analyzing element and the collimator, which enables the apparatus to be smaller. It is not necessary to decide the location of the slit to obtain high sensitive analyzing element.
As analyzing element monochromatic crystal such as lithium fluoride can be used, but artificial multi-layered grating can also be used.
The above object is attained by a second aspect of the present invention. The X-ray analysis apparatus makes analysis based on the detected result of the X-ray beam from the specimen. This X-ray analysis apparatus is provided with X-ray radiation source, analyzing element, collimator and X-ray detector. The X-ray radiation source radiates the primary X-ray beam. The analyzing element diffracts the primary X-ray beam from the X-ray radiation source to obtain monochromatic primary X-ray beam, and reflects the monochromatic primary X-ray beam toward the specimen. The collimator reflects the primary X-ray beam from the X-ray radiation source totally, and focuses on the specimen. The X-ray detector detects the X-ray beam from the specimen. The analyzing element is to be formed circularly having inner periphery which diffracts the primary X-ray beam. The collimator has the surface on which the primary X-ray beams are reflected totally. The collimator is placed in the internal space defined by the inner periphery of the analyzing element. The analyzing element and the collimator are so arranged that the axis of the annular analyzing element and that of the collimator can substantially coincide with each other.
The X-ray analysis apparatus, which the present invention is applied to, can make analysis of the X-ray fluorescence beam as well as diffracted X-ray beam. The analysis of the X-ray fluorescence beam is made by analyzing the element of the specimen by detecting the X-ray fluorescence beam generated from the specimen. The analysis of the diffracted X-ray beam is made to know the structure of the lattice from the angle of the diffraction of the diffracted X-ray beam.